557 lines
26 KiB
Ada
557 lines
26 KiB
Ada
------------------------------------------------------------------------------
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-- --
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-- GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS --
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-- --
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-- S Y S T E M . T A S K _ P R I M I T I V E S .O P E R A T I O N S --
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-- --
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-- S p e c --
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-- --
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-- Copyright (C) 1992-2020, Free Software Foundation, Inc. --
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-- --
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-- GNARL is free software; you can redistribute it and/or modify it under --
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-- terms of the GNU General Public License as published by the Free Soft- --
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-- ware Foundation; either version 3, or (at your option) any later ver- --
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-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE. --
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-- --
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-- As a special exception under Section 7 of GPL version 3, you are granted --
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-- additional permissions described in the GCC Runtime Library Exception, --
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-- version 3.1, as published by the Free Software Foundation. --
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-- --
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-- You should have received a copy of the GNU General Public License and --
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-- a copy of the GCC Runtime Library Exception along with this program; --
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-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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-- <http://www.gnu.org/licenses/>. --
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-- --
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-- GNARL was developed by the GNARL team at Florida State University. --
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-- Extensive contributions were provided by Ada Core Technologies, Inc. --
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-- --
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------------------------------------------------------------------------------
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-- This package contains all the GNULL primitives that interface directly with
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-- the underlying OS.
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with System.Parameters;
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with System.Tasking;
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with System.OS_Interface;
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package System.Task_Primitives.Operations is
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pragma Preelaborate;
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package ST renames System.Tasking;
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package OSI renames System.OS_Interface;
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procedure Initialize (Environment_Task : ST.Task_Id);
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-- Perform initialization and set up of the environment task for proper
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-- operation of the tasking run-time. This must be called once, before any
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-- other subprograms of this package are called.
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procedure Create_Task
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(T : ST.Task_Id;
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Wrapper : System.Address;
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Stack_Size : System.Parameters.Size_Type;
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Priority : System.Any_Priority;
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Succeeded : out Boolean);
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pragma Inline (Create_Task);
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-- Create a new low-level task with ST.Task_Id T and place other needed
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-- information in the ATCB.
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--
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-- A new thread of control is created, with a stack of at least Stack_Size
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-- storage units, and the procedure Wrapper is called by this new thread
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-- of control. If Stack_Size = Unspecified_Storage_Size, choose a default
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-- stack size; this may be effectively "unbounded" on some systems.
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--
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-- The newly created low-level task is associated with the ST.Task_Id T
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-- such that any subsequent call to Self from within the context of the
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-- low-level task returns T.
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--
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-- The caller is responsible for ensuring that the storage of the Ada
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-- task control block object pointed to by T persists for the lifetime
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-- of the new task.
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--
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-- Succeeded is set to true unless creation of the task failed,
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-- as it may if there are insufficient resources to create another task.
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procedure Enter_Task (Self_ID : ST.Task_Id);
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pragma Inline (Enter_Task);
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-- Initialize data structures specific to the calling task. Self must be
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-- the ID of the calling task. It must be called (once) by the task
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-- immediately after creation, while abort is still deferred. The effects
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-- of other operations defined below are not defined unless the caller has
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-- previously called Initialize_Task.
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procedure Exit_Task;
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pragma Inline (Exit_Task);
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-- Destroy the thread of control. Self must be the ID of the calling task.
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-- The effects of further calls to operations defined below on the task
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-- are undefined thereafter.
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----------------------------------
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-- ATCB allocation/deallocation --
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----------------------------------
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package ATCB_Allocation is
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function New_ATCB (Entry_Num : ST.Task_Entry_Index) return ST.Task_Id;
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pragma Inline (New_ATCB);
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-- Allocate a new ATCB with the specified number of entries
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procedure Free_ATCB (T : ST.Task_Id);
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pragma Inline (Free_ATCB);
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-- Deallocate an ATCB previously allocated by New_ATCB
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end ATCB_Allocation;
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function New_ATCB (Entry_Num : ST.Task_Entry_Index) return ST.Task_Id
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renames ATCB_Allocation.New_ATCB;
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procedure Initialize_TCB (Self_ID : ST.Task_Id; Succeeded : out Boolean);
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pragma Inline (Initialize_TCB);
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-- Initialize all fields of the TCB
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procedure Finalize_TCB (T : ST.Task_Id);
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pragma Inline (Finalize_TCB);
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-- Finalizes Private_Data of ATCB, and then deallocates it. This is also
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-- responsible for recovering any storage or other resources that were
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-- allocated by Create_Task (the one in this package). This should only be
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-- called from Free_Task. After it is called there should be no further
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-- reference to the ATCB that corresponds to T.
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procedure Abort_Task (T : ST.Task_Id);
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pragma Inline (Abort_Task);
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-- Abort the task specified by T (the target task). This causes the target
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-- task to asynchronously raise Abort_Signal if abort is not deferred, or
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-- if it is blocked on an interruptible system call.
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--
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-- precondition:
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-- the calling task is holding T's lock and has abort deferred
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--
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-- postcondition:
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-- the calling task is holding T's lock and has abort deferred.
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-- ??? modify GNARL to skip wakeup and always call Abort_Task
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function Self return ST.Task_Id;
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pragma Inline (Self);
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-- Return a pointer to the Ada Task Control Block of the calling task
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type Lock_Level is
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(PO_Level,
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Global_Task_Level,
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RTS_Lock_Level,
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ATCB_Level);
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-- Type used to describe kind of lock for second form of Initialize_Lock
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-- call specified below. See locking rules in System.Tasking (spec) for
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-- more details.
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procedure Initialize_Lock
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(Prio : System.Any_Priority;
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L : not null access Lock);
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procedure Initialize_Lock
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(L : not null access RTS_Lock;
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Level : Lock_Level);
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pragma Inline (Initialize_Lock);
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-- Initialize a lock object
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--
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-- For Lock, Prio is the ceiling priority associated with the lock. For
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-- RTS_Lock, the ceiling is implicitly Priority'Last.
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--
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-- If the underlying system does not support priority ceiling
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-- locking, the Prio parameter is ignored.
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--
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-- The effect of either initialize operation is undefined unless is a lock
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-- object that has not been initialized, or which has been finalized since
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-- it was last initialized.
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--
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-- The effects of the other operations on lock objects are undefined
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-- unless the lock object has been initialized and has not since been
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-- finalized.
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--
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-- Initialization of the per-task lock is implicit in Create_Task
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--
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-- These operations raise Storage_Error if a lack of storage is detected
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procedure Finalize_Lock (L : not null access Lock);
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procedure Finalize_Lock (L : not null access RTS_Lock);
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pragma Inline (Finalize_Lock);
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-- Finalize a lock object, freeing any resources allocated by the
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-- corresponding Initialize_Lock operation.
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procedure Write_Lock
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(L : not null access Lock;
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Ceiling_Violation : out Boolean);
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procedure Write_Lock (L : not null access RTS_Lock);
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procedure Write_Lock (T : ST.Task_Id);
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pragma Inline (Write_Lock);
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-- Lock a lock object for write access. After this operation returns,
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-- the calling task holds write permission for the lock object. No other
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-- Write_Lock or Read_Lock operation on the same lock object will return
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-- until this task executes an Unlock operation on the same object. The
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-- effect is undefined if the calling task already holds read or write
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-- permission for the lock object L.
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--
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-- For the operation on Lock, Ceiling_Violation is set to true iff the
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-- operation failed, which will happen if there is a priority ceiling
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-- violation.
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--
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-- For the operation on ST.Task_Id, the lock is the special lock object
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-- associated with that task's ATCB. This lock has effective ceiling
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-- priority high enough that it is safe to call by a task with any
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-- priority in the range System.Priority. It is implicitly initialized
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-- by task creation. The effect is undefined if the calling task already
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-- holds T's lock, or has interrupt-level priority. Finalization of the
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-- per-task lock is implicit in Exit_Task.
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procedure Read_Lock
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(L : not null access Lock;
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Ceiling_Violation : out Boolean);
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pragma Inline (Read_Lock);
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-- Lock a lock object for read access. After this operation returns,
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-- the calling task has non-exclusive read permission for the logical
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-- resources that are protected by the lock. No other Write_Lock operation
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-- on the same object will return until this task and any other tasks with
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-- read permission for this lock have executed Unlock operation(s) on the
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-- lock object. A Read_Lock for a lock object may return immediately while
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-- there are tasks holding read permission, provided there are no tasks
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-- holding write permission for the object. The effect is undefined if
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-- the calling task already holds read or write permission for L.
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--
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-- Alternatively: An implementation may treat Read_Lock identically to
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-- Write_Lock. This simplifies the implementation, but reduces the level
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-- of concurrency that can be achieved.
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--
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-- Note that Read_Lock is not defined for RT_Lock and ST.Task_Id.
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-- That is because (1) so far Read_Lock has always been implemented
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-- the same as Write_Lock, (2) most lock usage inside the RTS involves
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-- potential write access, and (3) implementations of priority ceiling
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-- locking that make a reader-writer distinction have higher overhead.
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procedure Unlock
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(L : not null access Lock);
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procedure Unlock (L : not null access RTS_Lock);
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procedure Unlock (T : ST.Task_Id);
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pragma Inline (Unlock);
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-- Unlock a locked lock object
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--
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-- The effect is undefined unless the calling task holds read or write
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-- permission for the lock L, and L is the lock object most recently
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-- locked by the calling task for which the calling task still holds
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-- read or write permission. (That is, matching pairs of Lock and Unlock
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-- operations on each lock object must be properly nested.)
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-- Note that Write_Lock for RTS_Lock does not have an out-parameter.
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-- RTS_Locks are used in situations where we have not made provision for
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-- recovery from ceiling violations. We do not expect them to occur inside
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-- the runtime system, because all RTS locks have ceiling Priority'Last.
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-- There is one way there can be a ceiling violation. That is if the
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-- runtime system is called from a task that is executing in the
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-- Interrupt_Priority range.
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-- It is not clear what to do about ceiling violations due to RTS calls
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-- done at interrupt priority. In general, it is not acceptable to give
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-- all RTS locks interrupt priority, since that would give terrible
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-- performance on systems where this has the effect of masking hardware
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-- interrupts, though we could get away allowing Interrupt_Priority'last
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-- where we are layered on an OS that does not allow us to mask interrupts.
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-- Ideally, we would like to raise Program_Error back at the original point
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-- of the RTS call, but this would require a lot of detailed analysis and
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-- recoding, with almost certain performance penalties.
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-- For POSIX systems, we considered just skipping setting priority ceiling
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-- on RTS locks. This would mean there is no ceiling violation, but we
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-- would end up with priority inversions inside the runtime system,
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-- resulting in failure to satisfy the Ada priority rules, and possible
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-- missed validation tests. This could be compensated-for by explicit
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-- priority-change calls to raise the caller to Priority'Last whenever it
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-- first enters the runtime system, but the expected overhead seems high,
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-- though it might be lower than using locks with ceilings if the
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-- underlying implementation of ceiling locks is an inefficient one.
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-- This issue should be reconsidered whenever we get around to checking
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-- for calls to potentially blocking operations from within protected
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-- operations. If we check for such calls and catch them on entry to the
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-- OS, it may be that we can eliminate the possibility of ceiling
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-- violations inside the RTS. For this to work, we would have to forbid
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-- explicitly setting the priority of a task to anything in the
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-- Interrupt_Priority range, at least. We would also have to check that
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-- there are no RTS-lock operations done inside any operations that are
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-- not treated as potentially blocking.
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-- The latter approach seems to be the best, i.e. to check on entry to RTS
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-- calls that may need to use locks that the priority is not in the
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-- interrupt range. If there are RTS operations that NEED to be called
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-- from interrupt handlers, those few RTS locks should then be converted
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-- to PO-type locks, with ceiling Interrupt_Priority'Last.
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-- For now, we will just shut down the system if there is ceiling violation
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procedure Set_Ceiling
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(L : not null access Lock;
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Prio : System.Any_Priority);
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pragma Inline (Set_Ceiling);
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-- Change the ceiling priority associated to the lock
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--
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-- The effect is undefined unless the calling task holds read or write
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-- permission for the lock L, and L is the lock object most recently
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-- locked by the calling task for which the calling task still holds
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-- read or write permission. (That is, matching pairs of Lock and Unlock
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-- operations on each lock object must be properly nested.)
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procedure Yield (Do_Yield : Boolean := True);
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pragma Inline (Yield);
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-- Yield the processor. Add the calling task to the tail of the ready queue
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-- for its active_priority. On most platforms, Yield is a no-op if Do_Yield
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-- is False. But on some platforms (notably VxWorks), Do_Yield is ignored.
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-- This is only used in some very rare cases where a Yield should have an
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-- effect on a specific target and not on regular ones.
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procedure Set_Priority
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(T : ST.Task_Id;
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Prio : System.Any_Priority;
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Loss_Of_Inheritance : Boolean := False);
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pragma Inline (Set_Priority);
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-- Set the priority of the task specified by T to Prio. The priority set
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-- is what would correspond to the Ada concept of "base priority" in the
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-- terms of the lower layer system, but the operation may be used by the
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-- upper layer to implement changes in "active priority" that are not due
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-- to lock effects. The effect should be consistent with the Ada Reference
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-- Manual. In particular, when a task lowers its priority due to the loss
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-- of inherited priority, it goes at the head of the queue for its new
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-- priority (RM D.2.2 par 9). Loss_Of_Inheritance helps the underlying
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-- implementation to do it right when the OS doesn't.
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function Get_Priority (T : ST.Task_Id) return System.Any_Priority;
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pragma Inline (Get_Priority);
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-- Returns the priority last set by Set_Priority for this task
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function Monotonic_Clock return Duration;
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pragma Inline (Monotonic_Clock);
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-- Returns "absolute" time, represented as an offset relative to an
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-- unspecified Epoch. This clock implementation is immune to the
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-- system's clock changes.
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function RT_Resolution return Duration;
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pragma Inline (RT_Resolution);
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-- Returns resolution of the underlying clock used to implement RT_Clock
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----------------
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-- Extensions --
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----------------
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-- Whoever calls either of the Sleep routines is responsible for checking
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-- for pending aborts before the call. Pending priority changes are handled
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-- internally.
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procedure Sleep
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(Self_ID : ST.Task_Id;
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Reason : System.Tasking.Task_States);
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pragma Inline (Sleep);
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-- Wait until the current task, T, is signaled to wake up
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--
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-- precondition:
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-- The calling task is holding its own ATCB lock
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-- and has abort deferred
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--
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-- postcondition:
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-- The calling task is holding its own ATCB lock and has abort deferred.
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-- The effect is to atomically unlock T's lock and wait, so that another
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-- task that is able to lock T's lock can be assured that the wait has
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-- actually commenced, and that a Wakeup operation will cause the waiting
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-- task to become ready for execution once again. When Sleep returns, the
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-- waiting task will again hold its own ATCB lock. The waiting task may
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-- become ready for execution at any time (that is, spurious wakeups are
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-- permitted), but it will definitely become ready for execution when a
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-- Wakeup operation is performed for the same task.
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procedure Timed_Sleep
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(Self_ID : ST.Task_Id;
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Time : Duration;
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Mode : ST.Delay_Modes;
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Reason : System.Tasking.Task_States;
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Timedout : out Boolean;
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Yielded : out Boolean);
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-- Combination of Sleep (above) and Timed_Delay
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procedure Timed_Delay
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(Self_ID : ST.Task_Id;
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Time : Duration;
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Mode : ST.Delay_Modes);
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-- Implement the semantics of the delay statement.
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-- The caller should be abort-deferred and should not hold any locks.
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procedure Wakeup
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(T : ST.Task_Id;
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Reason : System.Tasking.Task_States);
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pragma Inline (Wakeup);
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-- Wake up task T if it is waiting on a Sleep call (of ordinary
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-- or timed variety), making it ready for execution once again.
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-- If the task T is not waiting on a Sleep, the operation has no effect.
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function Environment_Task return ST.Task_Id;
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pragma Inline (Environment_Task);
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-- Return the task ID of the environment task
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-- Consider putting this into a variable visible directly
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-- by the rest of the runtime system. ???
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function Get_Thread_Id (T : ST.Task_Id) return OSI.Thread_Id;
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-- Return the thread id of the specified task
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function Is_Valid_Task return Boolean;
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pragma Inline (Is_Valid_Task);
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-- Does the calling thread have an ATCB?
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function Register_Foreign_Thread return ST.Task_Id;
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-- Allocate and initialize a new ATCB for the current thread
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-----------------------
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-- RTS Entrance/Exit --
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-----------------------
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-- Following two routines are used for possible operations needed to be
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-- setup/cleared upon entrance/exit of RTS while maintaining a single
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-- thread of control in the RTS.
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--
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-- These routines also replace the functions Lock/Unlock_All_Tasks_List
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procedure Lock_RTS;
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-- Take the global RTS lock
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procedure Unlock_RTS;
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-- Release the global RTS lock
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--------------------
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-- Stack Checking --
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--------------------
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-- Stack checking in GNAT is done using the concept of stack probes. A
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-- stack probe is an operation that will generate a storage error if
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-- an insufficient amount of stack space remains in the current task.
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-- The exact mechanism for a stack probe is target dependent. Typical
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-- possibilities are to use a load from a non-existent page, a store to a
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-- read-only page, or a comparison with some stack limit constant. Where
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-- possible we prefer to use a trap on a bad page access, since this has
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-- less overhead. The generation of stack probes is either automatic if
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-- the ABI requires it (as on for example DEC Unix), or is controlled by
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-- the gcc parameter -fstack-check.
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-- When we are using bad-page accesses, we need a bad page, called guard
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-- page, at the end of each task stack. On some systems, this is provided
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-- automatically, but on other systems, we need to create the guard page
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-- ourselves, and the procedure Stack_Guard is provided for this purpose.
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procedure Stack_Guard (T : ST.Task_Id; On : Boolean);
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-- Ensure guard page is set if one is needed and the underlying thread
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-- system does not provide it. The procedure is as follows:
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--
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-- 1. When we create a task adjust its size so a guard page can
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-- safely be set at the bottom of the stack.
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--
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-- 2. When the thread is created (and its stack allocated by the
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-- underlying thread system), get the stack base (and size, depending
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-- how the stack is growing), and create the guard page taking care
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-- of page boundaries issues.
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--
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-- 3. When the task is destroyed, remove the guard page.
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--
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-- If On is true then protect the stack bottom (i.e make it read only)
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-- else unprotect it (i.e. On is True for the call when creating a task,
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-- and False when a task is destroyed).
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--
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-- The call to Stack_Guard has no effect if guard pages are not used on
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-- the target, or if guard pages are automatically provided by the system.
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------------------------
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-- Suspension objects --
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------------------------
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-- These subprograms provide the functionality required for synchronizing
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-- on a suspension object. Tasks can suspend execution and relinquish the
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-- processors until the condition is signaled.
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function Current_State (S : Suspension_Object) return Boolean;
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-- Return the state of the suspension object
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procedure Set_False (S : in out Suspension_Object);
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-- Set the state of the suspension object to False
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procedure Set_True (S : in out Suspension_Object);
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-- Set the state of the suspension object to True. If a task were
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-- suspended on the protected object then this task is released (and
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-- the state of the suspension object remains set to False).
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procedure Suspend_Until_True (S : in out Suspension_Object);
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-- If the state of the suspension object is True then the calling task
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-- continues its execution, and the state is set to False. If the state
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-- of the object is False then the task is suspended on the suspension
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-- object until a Set_True operation is executed. Program_Error is raised
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-- if another task is already waiting on that suspension object.
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procedure Initialize (S : in out Suspension_Object);
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-- Initialize the suspension object
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procedure Finalize (S : in out Suspension_Object);
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-- Finalize the suspension object
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-----------------------------------------
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-- Runtime System Debugging Interfaces --
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-----------------------------------------
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-- These interfaces have been added to assist in debugging the
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-- tasking runtime system.
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function Check_Exit (Self_ID : ST.Task_Id) return Boolean;
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pragma Inline (Check_Exit);
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-- Check that the current task is holding only Global_Task_Lock
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function Check_No_Locks (Self_ID : ST.Task_Id) return Boolean;
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pragma Inline (Check_No_Locks);
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-- Check that current task is holding no locks
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function Suspend_Task
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(T : ST.Task_Id;
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Thread_Self : OSI.Thread_Id) return Boolean;
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-- Suspend a specific task when the underlying thread library provides this
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-- functionality, unless the thread associated with T is Thread_Self. Such
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-- functionality is needed by gdb on some targets (e.g VxWorks) Return True
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-- is the operation is successful. On targets where this operation is not
|
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-- available, a dummy body is present which always returns False.
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|
|
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function Resume_Task
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(T : ST.Task_Id;
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Thread_Self : OSI.Thread_Id) return Boolean;
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-- Resume a specific task when the underlying thread library provides
|
|
-- such functionality, unless the thread associated with T is Thread_Self.
|
|
-- Such functionality is needed by gdb on some targets (e.g VxWorks)
|
|
-- Return True is the operation is successful
|
|
|
|
procedure Stop_All_Tasks;
|
|
-- Stop all tasks when the underlying thread library provides such
|
|
-- functionality. Such functionality is needed by gdb on some targets (e.g
|
|
-- VxWorks) This function can be run from an interrupt handler. Return True
|
|
-- is the operation is successful
|
|
|
|
function Stop_Task (T : ST.Task_Id) return Boolean;
|
|
-- Stop a specific task when the underlying thread library provides
|
|
-- such functionality. Such functionality is needed by gdb on some targets
|
|
-- (e.g VxWorks). Return True is the operation is successful.
|
|
|
|
function Continue_Task (T : ST.Task_Id) return Boolean;
|
|
-- Continue a specific task when the underlying thread library provides
|
|
-- such functionality. Such functionality is needed by gdb on some targets
|
|
-- (e.g VxWorks) Return True is the operation is successful
|
|
|
|
-------------------
|
|
-- Task affinity --
|
|
-------------------
|
|
|
|
procedure Set_Task_Affinity (T : ST.Task_Id);
|
|
-- Enforce at the operating system level the task affinity defined in the
|
|
-- Ada Task Control Block. Has no effect if the underlying operating system
|
|
-- does not support this capability.
|
|
|
|
end System.Task_Primitives.Operations;
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